Signal separation techniques to provide robust spread spectrum signal decoding

ABSTRACT

A spread spectrum communications system includes an antenna array for receiving different summations of desired and undesired signals, and receivers are coupled to the antenna array. Each receiver operates based upon a respective channel code for de-spreading the desired and undesired signals for determining at least one desired signal associated with the respective channel code, and for combining the at least one desired signal and the undesired signals after the de-spreading. A processor is coupled to the receivers for forming a mixing matrix based upon the combined signals from each receiver, with entries on a diagonal of the mixing matrix corresponding to the desired signals and entries adjacent the diagonal corresponding to the undesired signals. The processor also processes the mixing matrix so that a level of the desired signals increases and a level of the undesired signals decreases. A demodulator is coupled to the processor for demodulating at least one desired signal.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/651,606 filed Feb. 10, 2005, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of communications, and moreparticularly, to a spread spectrum communications receiver.

BACKGROUND OF THE INVENTION

Spread spectrum communications techniques have found wide application inwireless communications networks. The main characteristic of thesetechniques is that the channel is subdivided into data streams viaorthogonal codes. In the ideal situation during signal reception thedesired signal has perfect correlation with itself and zero correlationwith all other signals, including time delayed versions of itself. Afterpassing through a de-spreader, the signal would be recovered having beendisturbed only by random noise:x _(k) =as _(k) +n.

In real environments, however, the signals are subject to channeldistortion and timing imperfections due to multiple path propagationcausing intermixing, which in turn decreases the orthogonality of thesignals. The de-spread signal ends up with mixed components of the othersignals as well as the desired one:

$x_{k} = {{\sum\limits_{j = 1}^{n}{a_{kj}s_{j}}} + n}$where the term a_(kk)s_(k) is the desired signal and the other terms areinterference:x _(k) =a _(kk) s _(k) +n ₁ +nwhere n₁ is the noise due to the interferers.

Currently, the de-spread signal is processed to determine the symbolswith the extraneous terms acting as additional noise. This degrades theresult leading to a potential undesirable error rate. High error ratesrequire the use of techniques to provide an adequate integrity to thedata stream.

One approach is to increase the use of error correcting codes, whichdecreases the effective data rate of the link. Another approach is todecrease the symbol rate, which also decreases the effective data rateof the link. Yet another approach is to use negative acknowledgment whenthe errors exceed the correction capability of the coding, which againdecreases the data rate of the link. Other approaches exploit multipatheither via MIMO or diversity techniques, which require more complicatedcircuitry and processing at both the transmitter and the receiver.

The above approaches thus tend to either decrease the data rate of thelink, or require more complicated implementations at both thetransmitter and receiver. Moreover, requiring implementation at both thetransmitter and receiver usually requires standardization, and thisleads to incompatibilities with existing radio access networks.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of thepresent invention to improve the decoding process for spread spectrumsignals.

This and other objects, features, and advantages in accordance with thepresent invention are provided by a receiver that removes some or all ofthe extraneous signals from a received aggregate before they areprocessed by the symbol decoding function. The effective signal tointerferer ratio is therefore reduced, allowing for a lower errorcorrecting allowance to the link.

Instead of just trying to extract the desired signal, the decoder willexamine a number of the spread spectrum signals:x=As+n.The s vector is made up of all the signals that the receiver has spreadspectrum code use knowledge. This could be either because the receiverknows which codes are in use (e.g., control channels, multiple datachannels in use by the device), is informed which codes are in use bythe network, has searched the code space and found them, or acombination of these possibilities.

Any remaining coded signals not in the set are treated as noise and areincluded in n. In some cases the number of interferers to be removed maybe less than the set of available codes. This would be possible if itwas found that certain codes produced interferer components sufficientlylow to not be a significant contributor to the error rate. Anotherreason would be an excessive time required to process the aggregate ifall the known codes were included. As before, any codes not included inthe creation of s would appear as an additional noise componentpresented to the symbol decoder.

Upon examining the individual received signals, it can be seen that theyare linear sums of all the transmitted signal streams. The matrixequation for all of the signals can be re-written asy=Wx=WAs+Wn=WAs+n′.

The mixing matrix is formed based upon the combined signals from eachreceiver, with entries on a diagonal of the mixing matrix correspondingto the desired signals and entries adjacent the diagonal correspondingto the undesired signals. The mixing matrix is processed so that a levelof the desired signals increases and a level of the undesired signalsdecreases.

Processing of the mixing matrix may be based on a knowledge based signalprocessing, such as a zero forcing (ZF) process or a minimum meansquared estimation (MMSE) process. Alternatively, the mixing matrixsignal processing may be based on a blind signal separation process.Three commonly used techniques that fall under blind signal separationare principal component analysis (PCA), independent component analysis(ICA), and singular value decomposition (SVD). A key factor is that thesignal processing is not performing classical signal separation, as thedesired signal for each row is already known. Instead, the signalprocessing is cleaning up the separated signals in each channel. Theactual signal separation is performed in the receivers based uponde-spreading codes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a spread spectrum communications system inaccordance with the present invention.

FIG. 2 is a more detailed block diagram of the receive side of thespread spectrum communications system shown in FIG. 1.

FIG. 3 is a more detailed block diagram of another embodiment of thereceive side of the spread spectrum communications system shown in FIG.1.

FIG. 4 is a more detailed block diagram of yet another embodiment of thereceive side of the spread spectrum communications system shown in FIG.1.

FIG. 5 is a block diagram of the receive side of a spread spectrumcommunications system operating based upon array deflection forproviding different summations of desired and undesired signals forsignal processing in accordance with the present invention.

FIG. 6 is a block diagram of the receive side of a spread spectrumcommunications system operating based upon path selection for providingdifferent summations of desired and undesired signals for signalprocessing in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout, and prime and double primenotations are used to indicate similar elements in alternativeembodiments.

A simplified block diagram of a spread-spectrum communications system 10will initially be discussed in reference to FIG. 1. The communicationssystem 10 includes a spread spectrum transmitter assembly 20 and aspread spectrum receiver assembly 40. In the transmitter assembly 20, amodulator 22 receives input data 24 and a channel code.

The channel code is provided by a channel code transmit generator 26 andis unique for each channel. The channel code runs at a much higher ratethan a data rate of the input data so that the modulated spread-spectrumoutput signal 30 occupies a much greater bandwidth than the signal'sbaseband information bandwidth.

The spread-spectrum output signal 30 is transmitted via an antenna array50 coupled to the transmitter assembly 20, and is received by an antennaarray 60 coupled to the receiver assembly 40. The antenna arrays 50, 60are not limited to any particular configuration, and may include one ormore antenna elements 52(1)-52(N) in the transmit array and one or moreantenna elements in the receive array 62(1)-62(N). Although the numberof antenna elements in the arrays 50, 60 is shown to be equal in number,they may be different depending on a particular implementation.

In addition to receiving the desired spread spectrum signal 30,undesired signals are also received. The undesired signals may be aresult of channel distortion and timing imperfections causingintermixing, which in turn decreases the orthogonality of the signals.

A de-spread and combiner block 44 in the receiver assembly 40 determinesthe desired spread spectrum signal for demodulation by a demodulator 47.The de-spread and combiner block 44 includes a correlator 45 and areceive channel code generator 46 for generating a channel code. Thechannel codes generated by the respective transmit and receive channelcode generators 26, 46 are identical. After demodulation, the desiredsignals are decoded by a decoder 48 to generate output data 49.

A more detailed block diagram of the receiver assembly 40 is provided inFIG. 2. The illustrated receiver assembly 40 comprises a plurality ofRake receivers 100(1)-100(k), with each Rake receiver comprising ffingers 102 for selecting f different multipath components of thereceived desired and undesired signals. A Rake receiver will begenerally referred to by reference 100. In the illustrated embodiment,f=3 for each Rake receiver 100, although the actual number of fingers102 may vary, and they may be different in each instance within the sameoverall receiver structure. In lieu of Rake receivers 100, standardreceivers may be used.

For each Rake receiver 100, each finger 102 comprises a correlator 45coupled to a channel code generator 46. The channel code generator 46generates a channel code delayed by different time frames as determinedby a delay equalizer 104. As part of the correlation process, thereceive channel code is delayed by 1 chip slice in order to find a matchwith the corresponding transmit channel code in the received signals.

When a peak 106 is provided in the output of the matched filter 108, thecorrelator 45 has found a match in terms of identifying the desiredsignal. Each Rake receiver 100 has a unique channel code as compared tothe channel codes in the other Rake receivers. Each channel codecorresponds to a different channel. For instance, there may be one ormore voice channels, and one or more data channels.

The output of the correlator 45 is broken down into I and Q components.Although this is not necessary, the I and Q components provide increasedresolution for the desired and undesired signals. The I and Q componentsfrom the correlator 45 are then provided to a phase rotator 110. Achannel estimator 112 also provides an estimate of the channel to thephase rotator 110.

During reception by the Rake receiver 100, the I and Q components rotatein the frequency spectrum. The I and Q components are raw data, and eventhough the raw data may be unknown, the phase rotator 110 rotates theraw data back to the location before their rotation. The rotation isbased upon a known training sequence in the data.

The output of the phase rotator 110 is provided to the delay equalizer104. In each Rake receiver 100, there are three different delays, onefor each finger 102. The delay equalizer 104 determines what the delayis among the signals from each finger 102. Once the respective delaysare determined, the signals can be adjusted accordingly so that they maybe combined.

Still part of the Rake receiver 100, the I and Q components from eachfinger 102 are combined. The I components are combined by a combiner 114to generate a combined I component. Likewise, the Q components arecombined by a different combiner 116 to generate a combined Q component.The I and Q components are the added together by an adder 118.

This process is repeated for each Rake receiver 100. The output fromeach adder 118 is provided to a signal processor 130. The signalprocessor 130 includes a mixing matrix module 132. The mixing matrixmodule 132 populates a mixing matrix based upon the combined signalsprovided by each Rake receiver 100. Each row of the mixing matrix has adominant signal and one or more non-dominate signals. The non-dominatesignals are the undesired or noise signals. The dominant signal in eachrow corresponds to the desired signal for that particular channel.

A mixing matrix signal processing module 134 processes the mixing matrixso that a level of the desired signal term increases and a level of theundesired signal terms decreases in each row of the matrix. In otherwords, the noise floor of the mixing matrix is decreased by movingenergy from the off-diagonals to the diagonals. The desired signals fordemodulation are then selected by a select streams module 136. Channels1 through channel K may be selected for demodulation.

The mixing matrix module 132, the mixing matrix signal processing module134 and the select streams module 136 may all be implemented in thesignal processor 130, as illustrated. A key factor is that the processor130 is not performing classical signal separation, as the desired signalfor each row is already known. Instead, the signal processor is cleaningup the separated signals in each channel. The actual signal separationis performed in the Rake receivers 100 based upon de-spreading codes.

Without the signal processor 130, the received signals would generallyrequire a greater amount of error correcting codes to overcome the noiselevels of the undesired signals. Individually none of the interferersmay be significant, but in aggregate, they degrade the signal-to-noiseratio of the desired signals significantly. Consequently, a greateramount of error correcting codes are transmitted in the desired signals,which in turn, lowers the overall effective data rate.

The mixing matrix signal processing may be based on a knowledge basedsignal processing, such as a zero forcing (ZF) process or a minimum meansquared estimation (MMSE) process. Alternatively, the mixing matrixsignal processing may be based on a blind signal separation process.Three commonly used techniques that fall under blind signal separationare principal component analysis (PCA), independent component analysis(ICA), and singular value decomposition (SVD).

As long as the desired and undesired signals received by the antennaarray 60 coupled to the Rake receiver 100 are independent in somemeasurable characteristic, and if their signal sums are linearlyindependent from each other, one or more of these signal processingtechniques may be used to enhance the desired signals from a mixture ofthe desired and undesired signals. The measurable characteristic isoften some combination of the first, second, third or fourth moments ofthe signals.

Based upon the signals selected by the select streams module 136, thedemodulator 47 demodulates the selected desired signals. The output ofthe demodulator 47 also provides information to an adjust encodingmodule 140. The adjust encoding module 140 provides feedback back to thetransmitter 20. The transmitter 20 will adjust the amount of errorcorrecting codes being transmitted to the receiver. If the signalprocessor 130 is improving the signal-to-noise ratios in the mixingmatrix, then the transmitter 20 can reduce the amount of errorcorrecting codes being transmitted to the receiver 40 as part of thedesired data. This in turn increases the effective overall data rate ofthe desired signals. Alternately or in combination, the transmittercould change the spreading factor, the data rate, modulationconstellation or any other means associated with the robustness of thesignal stream's ultimate decoding.

The rank of the mixing matrix for the receiver assembly 40 illustratedin FIG. 2 is less than or equal to the number of channel codes. For kRake receivers, there are k channels, which each channel having a uniquechannel code.

Another embodiment of the receiver assembly 40′ is illustrated in FIG.3. The respective combiners 114′, 116′ for each Rake receiver 100′ havebeen modified so that the combined I and Q components of the desired andundesired signals are not added together by the adder 118 shown in FIG.2. Instead, the combined I components and the combined Q components aretreated as separate entries into the mixing matrix module 132′ forpopulating the mixing matrix. As a result, the rank of the mixing matrixis less than or equal to 2 times the number of channel codes.

In addition, the output of the select streams module 136′ adds the I andQ components together via a respective adder 139′ for each channel forthe selected channels before the demodulation is performed by thedemodulator 47′.

Yet another embodiment of the receiver assembly 40″ is illustrated inFIG. 4. This embodiment is similar to the receiver assembly 40′illustrated in FIG. 3, except the respective combiners 114″, 116″ foreach Rake receiver 100″ have been modified so that the outputs therefromare based upon the I and Q components provided by each finger 102″. As aresult, the rank of the mixing matrix is less than or equal to 2 timesthe number of fingers f times the number of channel codes.

In other words, all of the I and Q components are kept separate forpopulating the mixing matrix. If all the desired and undesired signalscame in robustly, the mixing matrix module 132′ can easily build themixing matrix. In an actual environment, some of the I and Q componentsare better off being combined. Consequently, the number of I or Q valuesfrom the selective combiners 114″ and 116″ may actually collapse to onefor either or both I and Q.

In addition, the output of the select streams module 136″ provides the Iand Q components to a respective combiner 137″, 138″ for each channel.Each channel has an adder 139″ for adding the I and Q components foreach channel associated therewith prior to demodulation by thedemodulator 47″.

As discussed in great detail in U.S. patent application Ser. No.11/232,500, which is assigned to the current assignee of the presentinvention and is incorporated herein by reference in its entirety,different techniques may be used to increase the rank of the mixingmatrix. These techniques include different antenna array configurationsfor generating more than one antenna pattern for receiving differentsummations of the desired and undesired signals. Other techniquesinclude adding or replacing summations of the desired and undesiredsignals to further populate the mixing matrix. These techniques will bediscussed with reference to FIGS. 5 and 6.

There are a number of different embodiments of the receive antenna array60. The N antenna elements 62 may be correlated for forming a phasedarray. In another embodiment, the N antenna elements 62 may comprise atleast one active antenna element and up to N−1 passive antenna elementsfor forming a switched beam antenna. In addition, at least two of the Nantenna elements may be correlated with different polarizations.

The receive antenna array 60 may thus have a multiplier effect on thereceived different summations of the desired and undesired signals. Byincreasing the rank of the mixing matrix, the desired signals have agreater chance of being enhanced by the signal processor 130.

The other techniques that will now be discussed advantageously allowsthe rank of the mixing matrix to be further increased without having toincrease the number of N antenna elements 62 in the receive antennaarray 60.

A multiplier effect on the number of received different summations ofthe desired and undesired signals may be accomplished using one or acombination of the following. Array deflection involves changing theelevation of the antenna patterns for receiving additional summations ofthe desired and undesired signals. Path selection may be performed sothat all of the summations of the desired and undesired signals used topopulate the mixing matrix are correlated and/or statisticallyindependent.

A block diagram of the receive side of the spread spectrumcommunications system 10 operating based upon array deflection forproviding different summations of desired and undesired signals forsignal processing is provided in FIG. 5.

The receive antenna array 260 comprises N antenna elements 262 forgenerating N initial antenna patterns for receiving N differentsummations of the desired and undesired signals. The receive antennaarray 260 also comprises an elevation controller 241 for selectivelychanging an elevation of at least one of the N initial antenna patternsfor generating at least one additional antenna pattern so that at leastone additional different summation of the desired and undesired sourcesignals is received thereby.

The mixing matrix has a rank less than or equal to N times the number ofchannel codes plus the number of additional different summations of thedesired and undesired signals received using the additional antennapatterns.

A block diagram of the receive side of the spread spectrumcommunications system 10 operating based upon path selection forproviding different summations of desired and undesired signals forsignal processing is provided in FIG. 6.

The receive antenna array 360 comprises N elements 363 for forming atleast N antenna beams for receiving at least N different summations ofthe desired and undesired signals, with N being greater than 2. Acontroller 350 is connected to the antenna array 360 for selectivelyforming the at least N antenna beams.

The signal processor 330 also determines if the different summations ofthe desired and undesired signals are correlated or statisticallyindependent, and if not, then cooperates with the controller 350 forforming different antenna beams for receiving new different summationsof the desired and undesired signals to replace the different summationsof the desired and undesired signals that are not correlated orstatistically independent in the mixing matrix.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

1. A spread spectrum communications system comprising: an antenna arraycomprising N antenna elements for receiving different summations ofdesired and undesired signals, where N≧2; a plurality of receivers, eachreceiver coupled to said same antenna array and operating based upon arespective channel code for de-spreading the desired and undesiredsignals for determining at least one desired signal associated with therespective channel code, and combining the at least one desired signaland the undesired signals after the de-spreading; a processor coupled tosaid plurality of receivers for forming a mixing matrix based upon thecombined signals from each receiver, with entries on a diagonal of themixing matrix corresponding to the desired signals and entries adjacentthe diagonal corresponding to the undesired signals, and processing themixing matrix so that a level of the desired signals increases and alevel of the undesired signals decreases; and a demodulator coupled tosaid processor for demodulating at least one desired signal anddetermining an error rate of the at least one desired signal afterdemodulation, the error rate being used as feedback to a transmittertransmitting the at least one desired signal so that characteristics innew transmitted signals can be adjusted based upon the determined errorrate.
 2. A spread spectrum communications system according to claim 1wherein there are X channel codes associated with said plurality ofreceivers; and wherein a rank of the mixing matrix is ≦X, where X≧2. 3.A spread spectrum communications system according to claim 1 wherein ineach receiver, the de-spreading comprises separating the at least onedesired signal and the undesired signals into I and Q components, andthe combining comprises adding the I and Q components together beforethe mixing matrix is formed.
 4. A spread spectrum communications systemaccording to claim 1 wherein the characteristics in the new transmittedsignals to be adjusted comprise at least one of error detectionencoding, data rate, modulation type and spread factor.
 5. A spreadspectrum communications system according to claim 1 wherein there are Xchannel codes associated with said plurality of receivers; wherein N≧2so that each antenna element in said antenna array provides at least onelinear summation of the desired and undesired signals to said pluralityof receivers so that a rank of the mixing matrix≦N*X.
 6. A spreadspectrum communications system according to claim 1 wherein said Nantenna elements comprise N active antenna elements so that said antennaarray forms a phased array.
 7. A spread spectrum communications systemaccording to claim 1 wherein said N antenna elements comprise at leastone active antenna element and up to N−1 passive antenna elements forforming a switched beam antenna.
 8. A spread spectrum communicationssystem according to claim 1 wherein said N antenna elements comprise atleast two correlated antenna elements having different polarizations. 9.A spread spectrum communications system according to claim 1 whereinthere are X channel codes associated with said plurality of receivers;wherein said antenna array generates N initial antenna patterns forreceiving N different summations of the desired and undesired signals,said antenna array comprising an elevation controller for selectivelychanging an elevation of at least one of the N initial antenna patternsfor generating at least one additional antenna pattern so that at leastone additional different summation of the desired and undesired signalsis received thereby; the mixing matrix having a rank ≦N*X+the number ofadditional different summations of the desired and undesired signalsreceived using the additional antenna patterns.
 10. A spread spectrumcommunications system according to claim 1 wherein said antenna arrayforms at least N antenna beams for receiving at least N differentsummations of the desired and undesired signals, with N being greaterthan 2; further comprising a controller coupled to said antenna arrayfor selectively forming the at least N antenna beams; and wherein saidprocessor also determining if the different summations of the desiredand undesired signals are correlated or statistically independent, andif not, then cooperating with said controller for forming differentantenna beams for receiving new different summations of the desired andundesired signals to replace the different summations of the desired andundesired signals that are not correlated or statistically independentin the mixing matrix.
 11. A spread spectrum communications systemaccording to claim 1 wherein said processor processes the mixing matrixbased on at least one of principal component analysis (PCA), independentcomponent analysis (ICA), and single value decomposition (SVD).
 12. Aspread spectrum communications system according to claim 1 wherein saidprocessor processes the mixing matrix based on at least one of a zeroforcing (ZF) process, and a minimum mean squared estimation (MMSE)process.
 13. A spread spectrum communications system comprising: anantenna array comprising N antenna elements for receiving desired andundesired signals, where N_(≧)2; at least one Rake receiver coupled tosaid antenna array and comprising up to f fingers for selecting up to fdifferent multipath components of the received desired and undesiredsignals, where f>2, each Rake receiver operating based upon a respectivechannel code so that each finger performs the following de-spreading thedesired and undesired signals for determining at least one desiredsignal associated with the respective channel code, and separating theat least one desired signal and the undesired signals into I and Qcomponents; a processor coupled to said at least one Rake receiver forforming a mixing matrix based upon the I and Q components, with entrieson a diagonal of the mixing matrix corresponding to the I and Qcomponents of the desired signals and entries adjacent the diagonalcorresponding to the I and Q components of the undesired signals,processing the mixing matrix so that a level of the I and Q componentsof the desired signals increases and a level of the I and Q componentsof the undesired signals decreases, with the processing being based onat least one of principal component analysis (PCA), independentcomponent analysis (ICA), single value decomposition (SVD), a zeroforcing (ZF) process, and a minimum mean squared estimation (MMSE)process, and combining the I and Q components for at least one desiredsignal; and a demodulator coupled to said processor for demodulating theat least one desired signal.
 14. A spread spectrum communications systemaccording to claim 13 wherein there are X channel codes associated withsaid at least one Rake receiver, where X≧1; wherein the respective Icomponents from said f fingers in each Rake receiver are combined afterthe de-spreading into a single I component, and the respective Qcomponents from said f fingers in each Rake receiver are combined afterthe de-spreading into a single Q component; and wherein a wherein a rankof the mixing matrix is ≦2*X.
 15. A spread spectrum communicationssystem according to claim 13 wherein there are X channel codesassociated with said at least one Rake receiver, where X≧1; wherein therespective I components from said f fingers in each Rake receiver areeach provided to said processor for separate entries into the mixingmatrix, and the respective Q components from said f fingers in each Rakereceiver are provided to said processor for respective entries into themixing matrix; and wherein a wherein a rank of the mixing matrix is<2*f*X.
 16. A spread spectrum communications system according to claim13 wherein said demodulator determines an error rate of the at least onedesired signal after demodulation, the error rate to be used as feedbackto a transmitter transmitting the at least one desired signal so thatcharacteristics in new transmitted signals can be adjusted based uponthe determined error rate.
 17. A spread spectrum communications systemaccording to claim 16 wherein the characteristics in the new transmittedsignals to be adjusted comprise at least one of error detectionencoding, data rate, modulation type and spread factor.
 18. A spreadspectrum communications system according to claim 13 wherein there are Xchannel codes associated with said at least one Rake receiver; whereinN≧2 so that each antenna element in said antenna array provides at leastone linear summation of the desired and undesired signals to said atleast one Rake receiver so that a rank of the mixing matrix ≦N+X.
 19. Aspread spectrum communications system according to claim 13 wherein saidN antenna elements comprise N active antenna elements so that saidantenna array forms a phased array.
 20. A spread spectrum communicationssystem according to claim 13 wherein said N antenna elements comprise atleast one active antenna element and up to N−1 passive antenna elementsfor forming a switched beam antenna.
 21. A spread spectrumcommunications system according to claim 13 wherein said N antennaelements comprise at least two correlated antenna elements havingdifferent polarizations.
 22. A spread spectrum communications systemaccording to claim 13 wherein there are X channel codes associated withsaid at least one Rake receiver; wherein said antenna array generates Ninitial antenna patterns for receiving N different summations of thedesired and undesired signals, said antenna array comprising anelevation controller for selectively changing an elevation of at leastone of the N initial antenna patterns for generating at least oneadditional antenna pattern so that at least one additional differentsummation of the desired and undesired signals is received thereby; themixing matrix having a rank ≦N*X+the number of additional differentsummations of the desired and undesired signals received using theadditional antenna patterns.
 23. A spread spectrum communications systemaccording to claim 13 wherein said antenna array forms at least Nantenna beams for receiving at least N different summations of thedesired and undesired signals, with N being greater than 2, said antennaarray comprising a controller for selectively forming the at least Nantenna beams; and wherein said processor also determining if thedifferent summations of the desired and undesired signals are correlatedor statistically independent, and if not, then cooperating with saidcontroller for forming different antenna beams for receiving newdifferent summations of the desired and undesired signals to replace thedifferent summations of the desired and undesired signals that are notcorrelated or statistically independent in the mixing matrix.
 24. Aspread spectrum communications system comprising: an antenna arraycomprising N antenna elements for receiving different summations ofdesired and undesired signals, where N≧2; a plurality of receivers, eachreceiver coupled to said same antenna array and operating based upon arespective channel code for de-spreading the desired and undesiredsignals for determining at least one desired signal associated with therespective channel code, and combining the at least one desired signaland the undesired signals after the de-spreading; a processor coupled tosaid plurality of receivers for forming a mixing matrix based upon thecombined signals from each receiver, with entries on a diagonal of themixing matrix corresponding to the desired signals and entries adjacentthe diagonal corresponding to the undesired signals, and processing themixing matrix so that a level of the desired signals increases and alevel of the undesired signals decreases, with the processing beingbased on at least one of principal component analysis (PCA), independentcomponent analysis (ICA), single value decomposition (SVD), a zeroforcing (ZF) process, and a minimum mean squared estimation (MMSE)processor; and a demodulator coupled to said processor for demodulatingat least one desired signal.
 25. A spread spectrum communications systemaccording to claim 24 wherein there are X channel codes associated withsaid plurality of receivers; and wherein a rank of the mixing matrix is<X, where X>2.
 26. A spread spectrum communications system according toclaim 24 wherein in each receiver, the de-spreading comprises separatingthe at least one desired signal and the undesired signals into I and Qcomponents, and the combining comprises adding the I and Q componentstogether before the mixing matrix is formed.
 27. A spread spectrumcommunications system according to claim 24 wherein said demodulatordetermines an error rate of the at least one desired signal afterdemodulation, the error rate to be used as feedback to a transmittertransmitting the at least one desired signal so that characteristics innew transmitted signals can be adjusted based upon the determined errorrate.
 28. A spread spectrum communications system according to claim 27wherein the characteristics in the new transmitted signals to beadjusted comprise at least one of error detection encoding, data rate,modulation type and spread factor.
 29. A spread spectrum communicationssystem according to claim 24 wherein there are X channel codesassociated with said plurality of receivers; wherein N≧2 so that eachantenna element in said antenna array provides at least one linearsummation of the desired and undesired signals to said plurality ofreceivers so that a rank of the mixing matrix ≦N*X.
 30. A spreadspectrum communications system according to claim 24 wherein there are Xchannel codes associated with said plurality of receivers; wherein saidantenna array generates N initial antenna patterns for receiving Ndifferent summations of the desired and undesired signals, said antennaarray comprising, an elevation controller for selectively changing anelevation of at least one of the N initial antenna patterns forgenerating at least one additional antenna pattern so that at least oneadditional different summation of the desired and undesired signals isreceived thereby; the mixing matrix having a rank ≦N*X+the number ofadditional different summations of the desired and undesired signalsreceived using the additional antenna patterns.
 31. A spread spectrumcommunications system according to claim 24 wherein said antenna arrayforms at least N antenna beams for receiving at least N differentsummations of the desired and undesired signals, with N being greaterthan 2; further comprising a controller coupled to said antenna arrayfor selectively forming the at least N antenna beams; and wherein saidprocessor also determining if the different summations of the desiredand undesired signals are correlated or statistically independent, andif not, then cooperating with said controller for forming differentantenna beams for receiving new different summations of the desired andundesired signals to replace the different summations of the desired andundesired signals that are not correlated or statistically independentin the mixing matrix.